# Current measurement in control and monitoring of piezoelectric actuators

##### Ronkanen, P. (2008)

Ronkanen, P.

Tampere University of Technology

2008

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**Julkaisun pysyvä osoite on**

http://urn.fi/URN:NBN:fi:tty-200903041028

##### Tiivistelmä

This thesis discusses the usability of current measurement in controlling and monitoring piezoelectric actuators. Current measurement contains information about the actuator and its environment. This work presents methods for utilizing the information in several control applications used in microrobotics, such as displacement control and external force estimation. The importance of current measurement is also discussed in context with piezoactuator -related problems, such as self-heating.

After an introduction to the topic, an electromechanical model of a piezoelectric actuator is presented. The model summarizes the different effects and inputs that affect the output of piezoelectric actuators. The model is later utilized as basis for the development of more specialized models for several control applications.

This thesis presents several control schemes which utilize current measurement in displacement control. The control methods utilize inverse actuator models to estimate the current required for the actuator to move as desired. The experiment results are very good: hysteresis is less than 2% and drift about 1% of the motion range.

Force estimation without the use of force sensors is accomplished with an actuator model that approximates the present external force by combining information about the current, voltage and displacement. The measured displacement can be simultaneously utilized in feedback control, thus enabling precise microrobotic operations. The accuracy of the estimated force is within 10% of the force range, with an average inaccuracy of about 3%.

Current measurement can be used to estimate the self-heating of periodically actuated piezoactuators. Peak-to-peak current increases concurrently with increasing temperature. Experiments show that the current increase is 0.5% per one degree increase in actuator temperature. In addition, a compensation method is presented for the displacement changes induced by self-heating. The displacement error of the heated actuator is reduced to an average of one third when the proposed compensation is used.

This thesis discusses current measurement as a part of a self-diagnostic system. Current measurement has potential in diagnosing faults and monitoring the condition of piezoelectric actuators.

The experimental results achieved with several control applications indicate that the proposed electromechanical actuator model is feasible. Moreover, the results reveal that current measurement provides valuable information that can be utilized in displacement control, and force and self-heating estimation, among others. Consequently, the information obtained by current measurement can often be used to replace a sensor, thus decreasing the complexity of the system.

After an introduction to the topic, an electromechanical model of a piezoelectric actuator is presented. The model summarizes the different effects and inputs that affect the output of piezoelectric actuators. The model is later utilized as basis for the development of more specialized models for several control applications.

This thesis presents several control schemes which utilize current measurement in displacement control. The control methods utilize inverse actuator models to estimate the current required for the actuator to move as desired. The experiment results are very good: hysteresis is less than 2% and drift about 1% of the motion range.

Force estimation without the use of force sensors is accomplished with an actuator model that approximates the present external force by combining information about the current, voltage and displacement. The measured displacement can be simultaneously utilized in feedback control, thus enabling precise microrobotic operations. The accuracy of the estimated force is within 10% of the force range, with an average inaccuracy of about 3%.

Current measurement can be used to estimate the self-heating of periodically actuated piezoactuators. Peak-to-peak current increases concurrently with increasing temperature. Experiments show that the current increase is 0.5% per one degree increase in actuator temperature. In addition, a compensation method is presented for the displacement changes induced by self-heating. The displacement error of the heated actuator is reduced to an average of one third when the proposed compensation is used.

This thesis discusses current measurement as a part of a self-diagnostic system. Current measurement has potential in diagnosing faults and monitoring the condition of piezoelectric actuators.

The experimental results achieved with several control applications indicate that the proposed electromechanical actuator model is feasible. Moreover, the results reveal that current measurement provides valuable information that can be utilized in displacement control, and force and self-heating estimation, among others. Consequently, the information obtained by current measurement can often be used to replace a sensor, thus decreasing the complexity of the system.

##### Kokoelmat

- Väitöskirjat [3961]